The present invention relates to a wafer conveyor apparatus and a method for detecting the inclination of a wafer inside a wafer cassette which houses wafers, and for performing either wafer mount or alarm processing.
Conventionally, there are known many types of apparatus which, for example, take semiconductor wafers one at a time from a wafer cassette which houses a plural number of semiconductor wafers (such as 25 pieces, for example) and conveys them to a next process.
Not only this, such known wafer conveyor apparatus are provided with a gripper to a conveyor platform and the semiconductor wafer is loaded to the upper surface of the gripper and is held by it, and this status is maintained while the conveyor platform is moved so as to advance and retreat to and from the cassette and take the semiconductor wafers.
The following is a description of the case when such a conventional wafer conveyor apparatus is used to take semiconductor wafers housed in a wafer cassette, from that cassette.
As shown in the partial longitudinal sectional view of FIG. 13, a moving means (not shown) moves the wafer conveyor apparatus 10 in the direction of housing of the semiconductor wafers 60, and the gripper 14 which is mounted to the conveyor platform 12 are inserted between the semiconductor wafers 60 and the lower side of the semiconductor wafers 60 housed in the wafer cassette 40. After this, this status is maintained while a raising and lowering means (not shown) raises the conveyor platform 12 so that the gripper 14 is raised and the holding surface of the gripper 14 loads and holds the semiconductor wafer 60. Then, the wafer conveyor apparatus 10 is retreated from the wafer cassette 40 so that the semiconductor wafers 60 can be taken out one at a time. Moreover, as shown in the longitudinal sectional view of the wafer cassette 40 in FIG. 14, each of the semiconductor wafers 60 stored in the wafer cassette 40 is inserted into each step of the grooves 40a formed in the surfaces of the inner sides of both of the side walls of the wafer cassette 40 but there are slight discrepancies in the horizontal status of the semiconductor wafers 60 and they are housed inclined to to the grooves 40a.
Because of this, when the semiconductor wafers 60 are taken from the wafer cassette 40 by an automated wafer conveyor apparatus 10 as the means described above, there must first be prior confirmation that there is a semiconductor wafer 60 stored in each of the steps of the grooves 40a inside the wafer cassette 40. In order to do this, a conventional wafer conveyor apparatus is provided with a sensor means or the like for irradiating a light beam in the direction of wafer conveyance and also in the forward and rear directions of a wafer cassette 40 and so detect whether or not there is a semiconductor wafer 60 housed as expected inside the wafer cassette 40.
However, normally, many wafer cassettes 40 are used with respect to the one semiconductor manufacturing apparatus and, therefore, there is the problem that a sensor means must be provided for each wafer cassette 40 and that the cost of the entire semiconductor apparatus becomes extremely high.
In addition, as has been described above, the wafer cassette 40 is configured so that the semiconductor wafers 60 are inserted into, and stored in each step of the grooves 40a formed in the inner side surfaces of both of the side walls and so as shown by the reference numerals 60a and 60b of FIG. 14, the semiconductor wafers 60 may be inserted and housed at a slight angle.
Assuming that the wafers are at regulated positions at a fixed pitch and the sensor normally moves from the bottom to the top of the wafer cassette according to the number of semiconductor wafers housed, in a so-called mapping method when there is detection for whether or not there is a semiconductor wafer housed inside the grooves in the wafer cassette, the height or the protrusion (insertion) of the grippers for taking out the semiconductor wafer is normally constant with respect to the grooves of the wafer cassette.
Therefore, in cases such as these, when the semiconductor wafers 60a,60b are held and taken out from the wafer cassette 40 by an automated wafer conveyor apparatus 10, there is the problem that the strong rubbing against the surface of the grooves 40a into which the semiconductor wafers 60a, 60b are inserted generates dust.
Furthermore, in the worst case, there is also the danger that the semiconductor wafer itself may break.
In the light of the problems associated with a conventional wafer conveyor apparatus, the present invention has as an object the provision of a wafer conveyor apparatus that can detect the presence or absence of a semiconductor wafer inside a wafer cassette and which is to be conveyed, and a method using this wafer conveyor apparatus for performing the detection of the inclination of a wafer inside the wafer cassette.